Companies and consumers increasingly depend on computers to process, distribute, and play back high quality video content. Engineers use compression (also called encoding) to reduce the bit rate of digital video. Compression decreases the cost of storing and transmitting video information by converting the information into a lower bit rate form. Decompression (also called decoding) reconstructs a version of the original information from the compressed form. A “codec” refers to an encoder/decoder of digital video.
Decoding video content can be a relatively straightforward task when video is encoded in a manner expected and supported by a video decoder. However, when video is encoded in an unexpected and/or unsupported manner, or when encoded video is somehow altered, damaged, or used in an unexpected way, video decoding can be difficult or impossible.
Some video coding standards use a variety of picture types. For example, some picture types can be decoded without reference to other pictures in the video sequence, and are called reference pictures or key pictures. Other picture types depend on the presence of other pictures in order to be decoded, and are called predicted pictures. While a video coding standard may not require that encoded video begin with, or even include, a reference picture, video decoders implementing the standard may nevertheless be unable to decode video without a reference picture.
If encoded video does not begin with a reference picture, a video decoder may be unable to decode the video. If encoded video does not begin with a reference picture, but a reference picture is present later in the encoded video, a video decoder may be able to decode the video after reaching the reference picture. However, this may result in a long delay before display of the video begins.
Therefore, there exists ample opportunity for improvement in technologies related to decoding video.